DESCRIPTION: (APPLICANT'S DESCRIPTION) The specific aim of the Morphology Core is to provide technical assistance, training, expertise, and necessary service and supplies for structural examination of intact tissues affected by clinical and experimental GvHD, and to assess the efficacy of therapeutic intervention with the CD4 peptide analog and related engineered proteins at the level of target tissue. Emphasis is placed on light microscopy and specialized tissue embedding and sectioning necessary to insure the availability of conventional histology, immunohistochemistry, and in situ hybridization. In addition, specialized ultrastructure as well as TUNEL staining will be employed to enable detection of the earliest and most subtle changes of disease initiation and treatment response. Because the PI is both an anatomic pathologist as well as a dermatopathologist with a background in investigative pathology, both cutaneous and extracutaneous target tissues may be processed and evaluated in this Core. The specific aims are: 1. Assist in cellular and subcellular localization of peptide binding (Project 1) 2. Evaluate all murine tissues for GvHD pathology and peptide response using conventional and specialized in situ morphological approaches (Project 2). 3. Provide morphological expertise to confirm GvHD clinical diagnoses and to provide specialized analysis, where appropriate, of clinical biopsy specimens (Project 3).